Capacity type pickup



March 22, 1949. c. M. SINNETT 2,465,288 7 CAPACITY TYPE PICKUP Filed March 31, 1944 v Swen tor an mmzzMwmz/r Gttomeg Patented Mar. 22, 1949 tlNl'i'ED S TATE CAPACETY TYPE PICKUP of Delaware Application March 31, 1944, Serial No. 528,840

17 Claims.

This invention relates to signal translating apparatus, and more particularly to a signal translating device of the capacity type adapted for use especially in connection with phonograph records, the present invention having particular reference to the type of translating device disclosed and claimed in my copending application Serial No. 414,305, filed October 9, 1941, now Patent No. 2,376,456, granted May 22, 1945.

In the aforesaid copending application, there is disclosed a capacity type pickup which comprises a supporting member carrying a pair of electrodes in capacitive relation to each other, one of the electrodes being stationary and the other being mounted for movement relative to the stationary electrode. The movable electrode consists of a relatively thin, narrow, flexible strip of metal extending across the stationary electrode and anchored at both its ends. A needle is secured to the movable electrode substantially midway between its ends and is arranged to cooperate with the groove of a phonograph record. Movement of the movable electrode in response to the needle is confined substantially to a region in the vicinity of the needle to avoid vibration reflection from other parts of the movable electrode back toward the needle, thereby substantially eliminating distcrtion and extending the range over which the pickup is operated with great efficiency. A pickup device of this type is extremely light in weight, having a needle pressure of approximately 20 grams. Such a pickup may be connected in the tuning circuit of a suitable high frequency oscillator (for example, a 40 to 50 megacycle oscillator), and when the capacity of the pick-up is varied in response to the record, it produces a frequency shift in the oscillator circuit, and frequency modulation results. This may be passed through the regular FM channel of a radio receiver for reproduction.

The forms of pickup disclosed in my aforesaid copending application have a relatively wide frequency range of operation. In some cases, it is not necessary to provide so extensive a range as is afforded by the pickup constructions of my aforesaid copending application. In sacrificing some of this wide range, it is possible to modify the construction of the pickup so that it will also be less expensive. Accordingly, it is the primary object of my present invention to provide an improved capacity type pickup which is relatively inexpensive in cost and is especially useful in providing frequency modulation of an oscillator circuit wherein the pickup constitutes a tuning element.

More particularly, it is an object of my pres nt invention to provide an improved capacity type pickup as aforesaid which is relatively simple in construction, yet highly eflicient in use.

Another object of my present invention is to provide an improved capacity type pickup which will afford a comparatively large gain in signal to noise ratio.

Still another object of my present invention is to provide an improved capacity type pickup as aforesaid which will not cause the record with which it cooperates during reproduction to radiate extraneous sounds and which will not itself produce such sounds.

A further object of my present invention is to provide an improved capacity type pickup which will operate with a minimum of distortion.

Still another object of my present invention is to provide an improved capacity type pickup as above set forth in which the mass of the moving parts is very low.

A further object of my present invention is to provide an improved capacity type pickup which is very flexible in operation.

It is also an object of my present invention to provide an improved pickup de vice of the character set forth which is sturdy in construction, which is economical in cost, and which will have a long life.

In accordance with one form of my present invention, I provide a suitable supporting member which carries a pair of electrodes in capacitive relation to each other. One of the electrodes is stationary and the other electrode, which is made of a thin strip of resilient materiaL'is anchored at one end but freely suspended at its opposite end to thereby provide a movable portion which is swingable toward and away from the stationary electrode. If desired, the movable electrode may be formed with stiffening flanges along its longitudinal edges to thereby insure movement of the movable portion thereof as a whole and to prevent torsion of the strip. A needle is carried by the movable electrode for cooperation with the groove of a record, the movement imparted thereto by the record groove producing corresponding movement of the swingabl electrode relative to the stationary one to thereby vary the capacity of the pickup. In accordance with various modifications of this form of my present invention, the needle may be so mounted on the movable electrode that it will impart thereto movements proportional to the magnitude of movement imparted to it by the record, the movement of the active portion of the movable electrode in some cases being of lesser and in some cases of greater magnitude than that of the needle.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description of several embodiments thereof, when read in connection with the accompanying drawing, in which Figure 1 is a perspective view of one form of pickup device according to my present invention,

Figure 2 is a similar view of a modification thereof,

Figure 3 is a similar view of a still further modification of this form of my invention,

Figure 4 is a similar view of still another modification of this form of my invention, and

Figure 5 is a wiring diagram illustrating one circuit in connection with which my improved pickup may be used advantageously.

Referring more particularly to the drawing, wherein similar reference characters designate corresponding parts throughout, there is shown, in Fig. 1, a supporting block I of insulating material to which is secured a stationary electrode 3 comprising one electrode of the capacity pickup. Also mounted on the block I between a pair of brass plates or blocks 5 is a movable electrode 1 which cooperates with the stationary electrode 3, the electrode 1 being spaced from the electrode 3 by air or other suitable dielectric material. The electrode 1 is preferably made out of a strip of relatively narrow, thin piece of nickel-steel alloy or any other suitable material which is resilient and has a thickness of about 3 to 5 mils and a width of about inch.

The blocks 5 anchor one end of the movable electrode 1 and hingedly mount this electrode for swinging movement toward and away from the stationary electrode 3 due to the resilience of the electrode 1. The upper and lower longitudinal edges of the strip 1 may be bent out of the plane thereof to provide stiffening flanges 1a and lb which insure movement of the extending portion of the electrode 1 (that is, the portion to the left of the blocks 5) as a whole and prevent twisting or torsional movement thereof.

A needle 9 is secured to the strip 1, as by solder I3 01' the like, preferably at the bend line of the flange 1b thereof. The left hand end of the electrode 1 is freely suspended, and the needle 9 extends therefrom in substantially the plane of the vertical body portion thereof. The needle 9 terminates in a record engaging tip I i which may be of sapphire or the like for long wear. Preferably, the major portion of the needle is rigid torsionally and is of the type disclosed in the Hasbrouck Patent No. 2,280,763. Such a needle may be made of piano wire or the like having a diameter of the order of 10 to 12 mils and a length of about inch to inch.

The stationary electrode 3 may be connected by means of a lead [5 to the inner conductor I! of a concentric transmission line. The movable electrode 1 may be connected by a lead [9 to the outer, tubular conductor 2! of the aforesaid transmission line, the tube 2| being also utilized as a pickup arm, if desired.

A pickup device such as that described above may be employed to control the frequency of any tuned circuit and finds its particular application in modulating an oscillator in any suitable phonograph reproducing circuit, such as those more particularly disclosed and claimed in my copending application Serial No. 459,375, filed September 23, 1942. By way of illustration, reference is made to Fig. "I, wherein the pickup device is connected to an oscillator comprising a suitable oscillator tube 23 provided with an oscillator tuning inductance 25. The pickup capacitor 3, 1 is shunted across the inductance 25 and is connected therewith through a shielded cable which may be obtained, for example, by grounding the pickup arm 2|. The capacity of the shielded cable should be relatively low with respect to that of the pickup 3, 1. The output circuit 21 of the oscillator tube 23 is provided with a tuned circuit 29 which may be tuned to resonance with the desired oscillation mid-frequency. The variation of the capacity at the pickup will cause the oscillation frequency to vary above and below the normal frequency, thereby resulting in a frequency modulated signal which is delivered to a suitable output circuit and may be utilized in any suitable manner, as to operate a loudspeaker or the like (not shown).

The form of my invention shown in Fig. 2 is similar to that shown in Fig. 1 except that the movable electrode 1 is triangular in shape, being anchored by the blocks 5 at its large or base end. The freely suspended end thereof extends somewhat past the fixed electrode 3, and only a region of the movable electrode 1 in the vicinity of the free or pointed end thereof cooperates with the fixed electrode 3. Here, again, the needle 9 extends from the free end of the electrode 1 in substantially the plane thereof.

With both forms of the invention described above, it is obvious that the magnitude of movement of the free end of the movable electrode 1 will not exceed the magnitude of movement imparted to the needle 9 by the record groove. To provide greater sensitivity, the modifications shown in Figs. 3 and 4 are provided. Fig. 3 employs a triangular or tapered, movable electrode 1 similar to that of Fig. 2, and Fig. 4 employs a strip electrode similar to that of Fig. 1. In Fig. 3, the needle 9 is secured to the movable electrode 7 at a point intermediate the region of the electrode 1 which cooperates with the stationary electrode 3 and the anchored end thereof. Thus, a step-up ratio is obtained between the magnitude of movement of the needle 9 in response to the record and the magnitude of movement of the region of the movable electrode 7 near the freely suspended end thereof which cooperates with the stationary electrode 3. In this way, increased sensitivity is obtained. In the construction of Fig. 4, the needle 9 is also mounted at a point intermediate the ends of the movable electrode, the stationary electrode 3 being arranged to cooperate with an intermediate portion of the movable electrode 1 to provide a similar step-up ratio.

Although I have shown several forms of my present invention and have described the same with great detail, it will undoubtedly be apparent to those skilled in the art that many other modifications of my present invention, as well as changes in those described, are possible without departing from the spirit of the invention. For example, in the form illustrated in Figs. 2 and 3, the movable electrode 1 may be made other than triangular in shape, and it may be made to diverge away from the mounting blocks toward the freely suspended end thereof, instead of converging from the anchoring blocks 5 toward its freely suspended end. Also, instead of securing the needle 9 to the body or vertical portion of the movable electrode 7, it may be secured to the lower flange lb. Other changes will, no doubt, readily suggest themselves to those skilled in the art. I therefore desire that my invention shall not be limited except insofar as is made necessary by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. A phonograph record signal translating device comprising a pair of cooperating electrodes spaced from each other by a dielectric and constituting a capacitor, one of said electrodes being mounted for movement of at least a portion thereof toward and away from the other of said electrodes, said movable portion of said one electrode terminating in a freely suspended end and including at least one iiange element for constraining said movable portion of said one eiectrode against twisting, and a needle carried by said first named electrode at said portion for co operation with a record, the movement of said needle in response to the record imparting movement to said movable electrode whereby to vary the capacitance of said capacitor.

2. A phonograph record signal translating device comprising a pair of cooperating electrodes spaced from each other by a dielectric and constituting a capacitor, one of said electrodes being mounted for movement of at least a portion thereof toward and away from the other of said electrodes, said movable portion of said one electrode terminating in a freely suspended end and including flange means extending along said electrode for constrainin said movable portion of said one electrode against twisting, and a needle carried by said first named electrode adjacent said freely suspended end thereof for cooperation with a record, the movement of said needle in response to the record imparting movement to said movable electrode whereby to vary the capacitance of said capacitor.

3. A phonograph record signal translating device comprising a pair of cooperating electrodes spaced from each other by a dielectric and con stituting a capacitor, one of said electrodes being hingedly mounted for swinging movement of at least a portion thereof toward and away from the other of said electrodes, said movable portion of said one electrode terminating in a freely suspended end and including flange means for constraining said movable portion of said one electrode against twisting, and a needle carried by said first named electrode at said portion for cooperation with a record, the movement of said needle in response to the record imparting movement to said movable electrode whereby to vary the capacitance of said capacitor.

4. A phonograph record signal translating device comprising a pair of cooperating electrodes spaced from each other by a dielectric and constituting a capacitor, one of said electrodes being hingedly mounted at one end and having its opposite end freely suspended whereby to provide a swingable portion for swinging movement toward and away from the other of said electrodes, said swingable portion including at least one flange element extending alon said portion for constraining said swingable portion against twisting and a needle carried by said swingable portion for cooperation with a record, the movement of said needle in response to the record imparting movement to said swingable portion whereby to vary the capacitance of said capacitor.

5. A translating device according to claim 4 wherein said movable electrode comprises a strip of resilient, electrically conductive material, said strip being anchored adjacent said one end, and the resilience of said material affording the hinge action.

6. A translating device according to claim 4 wherein said movable electrodecomprises a strip of resilient, electrically conductive material, and characterized further in that said needle is disposed substantially in the plane of said strip.

7. A translating device according to claim 4 wherein said needle is carried by said movable electrode adjacent said freely suspended end thereof.

8. A translating device according to claim 4 wherein said movable electrode comprises a strip resilient, electrically conductive material, and characterized further in that said needle is carried by said strip adjacent said freely suspended end thereof, said needle extending from said end in substantially the plane of said strip.

9. A phonograph record signal translating device comprising a pair or cooperating electrodes spaced from each other by a dielectric and constituting a capacitor, one of said electrodes being hingedly mounted at one end and having its opposite end freely suspended wherebyto provide a swingable portion for swinging movement toward and away from other of said electrodes, said swingable portion including flange means extending alon said portion for constraining said swingable portion against twisting, and a needle carried by said swingable portion at a point intermediate the ends of said hingedly mounted electrode for cooperation with a record, the movement of said needle in response to the record imparting movement to said swingable portion whereby to vary the capacitance of said capacitor.

10. A phonograph record signal translating device comprising a pair of cooperating electrodes spaced from each other by a dielectric and constituting a capacitor, one of said electrodes com prising a strip of resilient, electrically conductive material hingedly mounted at one end and having its opposite end freely suspended whereby to provide a swingable portion for swinging movement toward and away from the other of said electrodes, said swingable portion including flange means extending along said. portion for constraining said swingable portion against twisting, and a needle carried by said strip at a point intermediate the ends thereof for cooperation with a record, said needle extending from said strip in substantially the plane of said strip, and the movement of said needle in response to the record imparting movement to said swingable portion whereby to vary the capacitance of said capacitor.

11. A phonograph record signal translating device comprising a pair of cooperating electrodes spaced from each other by a dielectric and constituting a capacitor, one of said electrodes being hingedly mounted at one end and having its opposite end freely suspended whereby to provide a swingable portion for swinging movement toward and away from the other of said electrodes, said swingable portion including at least one flange element for constraining said swingable portion against twisting, said electrodes being so related that only a region of said movable electrode in the vicinity of its freely suspended end cooperates 7 with said other electrode, and a needle carried by said swingable portion for cooperation with a record, the movement of said needle in response to the record imparting movement to said swingable portion whereby to vary the capacitance of said capacitor.

12. A translating device according to claim 11 characterized in that said needle is carried by said movable electrode at a point intermediate said region and said hinge whereby the magnitude of movement of said region in response to movement of said needle is amplified relative to the magnitude of movement of said needle in response to the record.

13. A phonograph record signal translating device comprising a pair of cooperating electrodes spaced from each other by a dielectric and constituting a capacitor, one of said electrodes being hingedly mounted at one end and having its opposite end freely suspended whereby to provide a swingable portion for swinging movement toward and away from the other of said electrodes, said swingable portion including flange means for constraining said swingable portion against twisting, said electrodes being so related that only a region of said movable electrode in termediate the ends thereof cooperates with said other electrode, and a needle carried by said swingable portion for cooperation with a record, the movement of said needle in response to the record imparting movement to said swingable portion whereby to vary the capacitance of said capacitor.

14. A translating device according to claim 13 characterized in that said needle is carried by said movable electrode at a point intermediate said region and said hinge whereby the magnitude of movement of said region in response to movement of said needle is amplified relative to the magnitude of movement of said needle in response to the record.

15. A phonograph record signal translating device comprising a pair of cooperating electrodes spaced from each other by a dielectric and constituting a capacitor, one of said electrodes being hingedly mounted at one end and having its opposite end freely suspended whereby to provide a swingable portion for swinging movement toward and away from the other of said electrodes, said swingable portion including flange means for constrainin said swingable portion against twisting, said movable electrode tapering ina direction from said hinged end thereof toward said freely suspended end thereof, and a needle carried by said swingable portion for cooperation with a record, the movement of said needle in response to the record imparting movement to said swingable portion whereby to vary the capacitance of said capacitor.

16. A phonograph record signal translating device comprising a pair of cooperating electrodes spaced from each other by a dielectric and constituting a capacitor, one of said electrodes being hingedly mounted at one end and having its opposite end freely suspended whereby to provide a swingable portion for swinging movement toward and away from the other of said electrodes, said swingable portion including flange means for constraining said swingable portion against twisting, said movable electrode tapering convergingly from substantially said hinged end thereof toward said freely suspended end thereof, and a needle carried by said swingable portion for cooperation with a record, the movement of said needle in response to the record imparting movement to said swingable portion whereby to vary the capacitance of said capacitor.

17. A phonograph record signal translating device comprising a pair of cooperating electrodes spaced from each other by a dielectric and constituting a capacitor, one of said electrodes comprisin a strip of resilient material hingedly mounted at one end and having its opposite end freely suspended whereby to provide a swingable portion for swinging movement toward and away from the other of said electrodes, said swingable portion being provided with flange means for rendering it relatively stiff in the direction of swinging movement thereof, and a needle carried by said swingable portion for cooperation with a record, the movement of said needle in response to the record imparting movement to said swingable portion whereby to vary the capacitance of said capacitor.

CHESTER M. SINNETT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,992,727 Thomas Feb. 26, 1935 2,147,092 Dudek Feb. 14, 1939 2,319,622 Meissner May 18, 1943 2,361,664 Stone Oct. 31, 1944 2,368,052 Unger Jan. 23, 1945 FOREIGN PATENTS Number Country Date 310,762 Great Britain Apr. 30, 1929 

